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Chapter 5

PSY100 Psychological Science (3rd Ed.) Textbook Notes Chapter 5

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Alison Luby

CHAPTER 5 – SENSATION AND PERCEPTION Sensation -Sensation: the sense organs’ response to external stimuli and the transmission of these responses to the brain -Perception: the processing, organization, and interpretation of sensory signals; it results in an internal representation of the stimulus -Sensory Coding: sensory organs’ translations of stimuli’s physical properties into neural impulses (brain cannot process raw stimuli)  Begins w/ transduction: process by which sensory receptors produce neural impulses when they receive physical/chemical stimulation  Sensory information is first sent to thalamus (except smell), then sent to cortex for interpretation -qualitative information about stimulus determined b/c different sensory receptors respond to qualitatively different stimuli; quantitative differences in stimuli are coded by the speed of a particular neuron’s firing (faster firing neuron is responding to a brighter light, louder sound, etc.) -receptors in sensory systems provide course coding: sensory qualities are coded by only a few different types of receptors, each of which responds to a broad range of stimuli; combined responses by different receptors firing at different rates allow us to tell difference between lime green and forest green, etc. Psychophysics -psychophysics (Weber and Fechner) examines our psychological experiences of physical stimuli (e.g. how much physical energy is required for sense organs to detect stimulus, etc.) Sensory Threshold -Absolute threshold: minimum intensity of stimulation that must occur before you experience sensation; the stimulus intensity detected above chance.  The level of intensity at which participants correctly detect a stimulus on 50% of the trials in which it is presented -Difference threshold: the minimum amount of change required for a person to detect a difference b/w two stimuli  Weber’s law: the noticeable difference b/w two stimuli is based on a proportion of the original stimulus, rather than a fixed amount of difference (ΔI/I = constant) Signal Detection Theory -early psychophysicists ignored human judgment on noticing stimulus -signal detection theory: theory of perception based on the idea that the detection of a faint stimulus required a judgment (not an all-or-none response) -research on signal detection produces payoff matrices w. four outcomes: hit, miss, false alarm, correct rejection  “Yea-sayers” biased towards reporting signal; “Nay-sayers” biased toward denying signal  Response bias refers to participant’s tendency to report detecting signal in ambiguous trial Sensory Adaptation -Sensory Adaptation : a decrease in sensitivity to a constant level of stimulation; when stimulus is presented continuously, the response of the sensory systems that detect it diminish over time Basic Sensory Processes Taste (Gustation) -taste receptors are part of the taste buds mostly on the tongue in structures called papillae but also on mouth and throat (spread uniformly throughout) -taste receptors send signal to cranial nerve to the thalamus -five qualities of taste: sweet, sour, salty, bitter, umami (arises from detection of glutamate, excitatory neurotransmitter) -supertasters have six times as many taste buds; highly aware of textures and flavours -mothers pass their eating preferences on to their offspring by eating behaviors before and immediately following birth (e.g. through breast milk) Smell (Olfaction) -odorants come into contact w/ olfactory epithelium (thin layer of tissue within nasal cavity that is embedded with smell receptors) -receptors transmit information to the olfactory bulb (brain centre for smell)  prefrontal cortex (whether smell is pleasant or aversive) and amygdala (for smell intensity) -women better than men for identifying odors but humans are bad at identifying odors by name -impaired sense of smell is associated with increased risk of mental decline and Alzheimer’s disease Touch (Haptic Sense) -conveys sensations of temperature, pressure, pain, and sense of where our limbs are in space -tactile stimulation caused by anything that makes contact w/ skin -receptors beneath skin send signals to thalamus along the trigeminal nerve (for touch above neck) or spinal nerve (for touch below neck) Pain -nerve fibres that convey pain information are thinner than nerves for temperature/pressure and found in all body tissues that sense pain: muscles, skin, organs, membranes around bone and joints, etc. -Fast nerve fibres for sharp, immediate pain and slow fibres for chronic, dull, steady pain  Myelinated axons respond quickly (myelination speeds neural signals); nonmyelinated axons respond slowly -Gate Control Theory: states that for us to experience pain, pain receptors must be activated and a neural “gate” in the spinal cord must allow the signals through the brain  Pain signals are transmitted by nerve fibres that can be blocked at the level of spinal cord by firing of larger sensory nerve fibres (“close the gate”) – e.g. scratching an itch, rubbing an aching muscle to reduce ache  Worrying/ focusing on pain stimulus opens the pain gates wider -females are more sensitive to pain than males are (proven with studies w/ autonomic responses, not under voluntary control) -two areas in brain for perception of pain: one area for responding to sensory input from body part that is in pain; the other part for registering the emotional aspect of pain (e.g. how unpleasant it is) Hearing/Audition -sound wave: pattern of changes in air pressure through time that results in the perception of sound; amplitude determines loudness; frequency determine pitch (e.g. high frequency = higher in pitch) -changes in air pressure arrive at outer ear  detected by eardrum (tympanic membrane) middle ear  vibrations transferred to ossicles ( bones called hammer, anvil, stirrup)  oval window (membrane of cochlea)  cochlea/inner ear (fluid-filled tube shaped like a snail)  basilar membrane (waves in fluid cause hair cells to bend and cause neurons on the basilar membrane to fire)  auditory nerves to thalamus the brain’s primary auditory cortex -hair cells are the primary auditory receptors -humans draw on the intensity and timing of sounds to locate where sounds are coming from Vision -light passes through cornea  refracts light an bent by lens, focusing light to form image on retina -pupil is small opening in front of lens and either contracts/dilates to determine how much light enters eyes (iris muscular circle changes shape to control pupil size) -accommodation: muscles change shape of lens (flat for distant object and thick for closer objects) -retina has two type of receptor cells: rods (for low levels of illumination; result in black and white perception; for night vision) and cones (result in color perception) -photopigments within rods and cones initiate transduction of light waves into neural impulse -fovea: centre of retina, where cones are densely packed -rods are located at retina’s edges, none in fovea -transduction of light into neural impulse by rods and cones  bipolar, amacrine and horizontal cells  ganglion cells (first cells in visual pathway to generate action potentials)  signals are passed through axons of ganglion cells to thalamus  visual info goes to the primary visual cortex (left and right visual cortex) -axons are gathered in bundle called optic nerve which exits the eye at the back of the retina; blind spot occurs in each eye at the point where optic nerve exits the retina (no rods or cones) -at optic chasm, half the axons in optic nerves cross; info from left side of visual space is projected to brain’s right hemisphere, etc. -receptive field: the population of sensory receptors that influence activity in a sensory neuron, the region within which the cell responds to given stimulus (located on a specific region of the retina) -lateral inhibition: visual process in which adjacent photoreceptors tend to inhibit one another; vis
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